The present invention relates to a magnetic bubble domain memory device. More particularly, the present invention relates to a magnetic bubble domain swap gate circuit for exchanging a magnetic bubble domain between a major loop acting as an information transmission line and a minor loop acting as an information storage loop.
In electronic computers, the reduction of dimensions and the increase of processing speeds have recently been remarkably accelerated by prominent developments in electronic techniques, such as the technique of semiconductor integrated circuits. Furthermore, the reliability of electronic computers has been remarkably improved by the adoption of solid state circuit elements. With the recent developments, memory capacities have been increased year after year, and reduction of the unit price necessary for memory devices and shortening of the access time have eagerly been sought in the art.
A non-volatile large-capacity memory device having a high reliability is necessary for storing and holding reliably a large quantity of information but it is impossible to fabricate such a memory device using volatile semiconductor storage elements. Furthermore, although a magnetic tape device or magnetic disk device is non-volatile, such devices have a fatal defect in that they involve movable parts. Accordingly, such memory devices are not capable of satisfying the requirement of high reliability. On the other hand, magnetic bubble devices have been widely used as non-volatile large-capacity memory devices having high reliability.
When a bias magnetic field of an appropriate amplitude is vertically applied to the surface of a thin magnetic layer having a uniaxial magnetic anisotropy, such as a thin layer of garnet or orthoferrite, a cylindrical magnetic domain, that is, a so-called "magnetic bubble," is produced. Practical applications for magnetic bubble devices, for performing storage of information and logic operations by utilizing such magnetic bubbles, have been rapidly developed in the fields where characteristics of these magnetic bubble devices (such as non-volatility, solid state of entire elements, the possibility of increased capacity and relatively high speed) are desired.
A magnetic bubble device is required to have the functions of generation, propagation, replication, gate circuit, stretch, detection and annihilation of magnetic bubbles. Furthermore, the device should have bias magnetic field applying means for making a magnetic bubble stable in the thin magnetic layer and rotating magnetic field applying means for transferring the magnetic bubble in the thin magnetic layer to the base of a magnetic pattern formed on the thin magnetic layer. Such a magnetic bubble memory device is disclosed in, for example, D. C. Bullock et al., Design and Fabrication of Large Capacity Bubble Memory Devices, IEEE Transactions on Magnetics, Vol. MAG. 15, No. 6, November 1979.
A magnetic bubble domain swap gate circuit used in such a conventional magnetic bubble memory device, in which the diameter of the magnetic domain is now remarkably reduced, involves various problems. More specifically, in the conventional magnetic bubble device, in order to increase the density it is necessary to reduce the diameter of the bubble domain, and with this reduction, it becomes necessary to reduce the dimensions of the permalloy patterns constituting the loops for transmission of the magnetic bubble domains and also to reduce the distance between every two permalloy patterns. Accordingly, the region for forming the magnetic bubble domain swap gate circuit is inevitably diminished, and it is difficult to increase the pattern width of the transmission control conductor pattern beyond a certain value. If the pattern width of the transmission control conductor pattern is narrowed, in order to inhibit the occurrence of ion migration or the like, it is inevitably necessary to reduce the density of the electric current to be supplied to the pattern. Therefore, the current capacity of the transmission control conductor pattern is reduced to such an extent that the necessary operational margin can hardly be obtained.